Honeywell 900 - Setpoint Scheduler; Overview; Table 37 SPS Inputs and Current State

Revision 9 900 Control Station User Guide 133
May 2014
Setpoint Scheduler
Overview
A setpoint schedule produces multiple setpoint outputs on a common time base. A setpoint schedule
contains multiple segments. Each segment contains multiple ramp or soak setpoints, multiple auxiliary soak
outputs, and multiple events. The last segment setpoint is always a soak (because there is no subsequent
setpoint to ramp to).
The Setpoint Scheduler can run any of the schedules in controller memory. Any schedule can be edited and
saved in one of the “slots” in the controller’s memory.
A Setpoint guarantee function (known as guaranteed hold) is provided that holds the Scheduler if a process
variable exceeds a predefined deviation from setpoint. Guaranteed hold is set on a per-segment basis and
can be set for high deviation, low deviation, high and low deviation, or none.
The schedule may be changed (with some exceptions) from the current state to a new state by the operator
as well as by inputs to the Scheduler function block in the controller configuration. Table 37 lists the
resulting states.
Table 37 SPS inputs and current state
Input Current State
READY HOLD RUN GHOLD STOP DISABLE
RESET READY READY RUN READY READY READY
HOLD HOLD HOLD HOLD HOLD STOP HOLD
RUN RUN RUN RUN GHOLD STOP RUN
GHOLD READY HOLD GHOLD GHOLD STOP READY
With regard to changing schedule state, if more than one function block input is on in the same execution
cycle, RESET has priority over HOLD and RUN, and GHOLD has priority over RUN.
Also, function block inputs will override inputs from the Control Station, which occur during the same
execution cycle. Finally, state changes from the Control Station are processed on the basis of the “last
change wins.”